In a recent article at Jalopnik, Jason Torchinsky (known in the internet auto enthusiast scene as “Torch”) explained how degraded but functional EV batteries could work great for school buses. In short, he suggests using low-cost conversion kits and reusing discarded batteries from other EVs to repower school buses, at a low cost.
While he’s known for his less-than-serious articles, like this one about using electric eels to power a Tesla Model 3, I think he’s really onto something with this idea. Also, I’m going to add a couple of ideas that could make EV school buses even more green.
The Basic Idea
Converting gas or diesel vehicles to run on batteries can be a big headache.
Take the original Tesla Roadster for example. The original plan was to purchase a slightly modified version of the Lotus Elise, share parts with other manufacturers, and take advantage of economies of scale even at low-volume production. During the design and engineering process, they had to change a thing here and a thing there to better accommodate the EV system, but it all added up. In the end, they only shared 8% of parts with the Elise and the vehicle cost far more than originally planned.
People converting cars to electric in their garages was the only way to get an EV until relatively recently, and is still a great way for the environmentally-oriented to keep older cars on the road. For older cars, like the original Volkswagen Beetle and Super Beetle, the conversion process isn’t that complicated. There’s not much in the way of electronics to deal with when converting. For newer cars, conversions get far more complicated, assuming you want to have things like a working speedometer. Regardless of age, though, finding nooks and crannies to put the battery cells in gets tough, and makes it hard to have a conversion with adequate range for most.
As Torchinsky points out, though, school buses are about as simple as a vehicle can get. You’ve basically got a diesel engine (occasionally gas), a transmission, a frame, a big and ugly metal box on top, and some seats bolted in. Under the bus between the frame rails, there’s tons of room for batteries, so energy density isn’t really a big deal. If that’s not enough, there’s also a lot of room under the hood (once the diesel engine is out) and lots of room under seats.
In these big spaces, you can install the worn battery packs, or cells from those packs, from other EVs as they come cheaply available. When a Tesla, LEAF, or Chevy Bolt loses too much range, the owner will either have the pack replaced or get rid of the car. The energy density has dropped, and there’s no more room for extra batteries to make up for the lost range. School buses, on the other hand, have room to take several such degraded packs and get the needed range.
But will this actually work?
The way school buses get used makes the idea even more workable. Sure, the average family sedan only goes a few dozen miles most days, but people don’t want a car with under 100 miles of range because they’re also occasionally used for longer highway trips. School buses don’t have that problem. They work a fixed route every school day, with average speeds of around 23 MPH and average lengths of around 32 miles. After working that route, the bus sits for 5-7 hours, and works the same route again. Then, the bus sits overnight.
Before anybody points out that buses are used for field trips out of town, or for away sporting events, take a closer look next time you see those buses. They’re often marked “Activity Bus,” and they tend to be larger diesel-pusher vehicles with two rear axles — kind of like a cheap version of a Greyhound bus. Yes, the activity buses are often used in a way that wouldn’t make them good candidates for a “redneck EV conversion,” so we can just leave those buses alone for now. As batteries come down in price, such buses could be replaced with EVs AND they may even be a good source for used batteries when the other buses need them.
Going back to the in-town buses, you basically couldn’t find a better use case for an EV with junkyard batteries. Yes, the bus is big and heavy, but it doesn’t go very fast and doesn’t go very far. To make those buses go 50-60 miles on a charge would probably require the cells from several degraded cars, and there’s plenty of room for that.
But what about charging?
Not a big problem. At all.
In the afternoon, the buses can charge on 220v and they have until the following morning to charge. There’s no rush. Once the morning run is done, they have several more hours to sit and charge. For routes where the overnight charge is sufficient for the morning run, but daytime charging isn’t enough for the afternoon, you’ll just need a bigger pack, which means more junkyard battery cells.
At the end of the day, it’s all about right-sizing the pack to the job that’s being done. Because the use of the bus is so predictable, it’s very easy to plan for.
Ways We Can Improve On This Concept
Reading the article gave me some other ideas that could prove useful. Or not. I’ll let the reader decide.
Living in the Southwest, the buses I grew up with and the ones my kids ride in don’t have heaters. They also don’t have air conditioning, which can be awful. Schoolbusfleet.com reports that the expensive EV buses in California generally do the same thing. If you skip the AC and heat, you don’t have to worry about impacts to range. I know from my travels, though, that you can’t get away with that in much of the country. The buses are going to need heaters in many places.
Currently, diesel school buses cycle engine coolant through pipes to a number of heater cores, just like a car. Each heater core has a blower fan, which circulates all of this leftover engine waste heat to safely warm the interior of the bus. But, take away the diesel engine, and you lose the heat source.
One option some New England districts are going for is just slamming a propane heater in. Yes, you lose the ability to brag on zero emissions, but the emissions from heating are much smaller than running a diesel drive engine. For converted buses, you can use a propane demand water heater to provide the existing coolant pipes and heater cores with hot water. Or, you could install a dedicated system. Either way, getting the heat from fossil fuels can be a good way to keep it warm without impacting range and driving up the cost of converting the buses to electric.
In places that get cold in the winter, but still have a lot of sunlight, solar heating systems could help reduce the use of heating fuel. The simplest way to do this is to put large black tubes on top of the bus and push air through them with fans. The sun heats the black tubes, which in turn heat the air pumped through them, which goes back into the bus. Some people do this with their homes and save a lot on their heating bill. There’s lots of room on top of a bus, so such a system is feasible.
All that space on the roof of the bus gives us another option for improvement: photovoltaic cells. For a normal length school bus, there’s about 8’x 35′ of roof, or about 280 square feet. Assuming 20 watts per square foot (for good quality, high efficiency cells in 2019), that’s around 5600w of max output. Cutting that in half for inefficiencies and losses still gives us 2800w of electricity for a vehicle that’s always left outside. On most days, the vehicle could probably generate 28 kWh of electricity. Assuming 2 miles per kWh, that gives about 56 miles of range per day.
For some routes, it may be possible to run the bus entirely on solar. For many others, it may be possible to put a serious dent in the electric bill with rooftop solar. Even better, the bus company or school district could probably have the cells installed with a power purchase agreement that gives a lower per-kWh price than the local utility company.
With cheap batteries, cheap conversion kits, and cheap electricity from solar power, it would make a lot of sense to start converting school bus fleets. This is an idea schools and bus companies should seriously consider.